CCNA Network Infrastructure and Connectivity Practice Question
Exhibit
SW1# show spanning-tree vlan 10
VLAN0010
Root ID Priority 32778
Address 0011.2233.4456
Bridge ID Priority 32778
Address 0011.2233.4456
SW2# show spanning-tree vlan 10
VLAN0010
Root ID Priority 32778
Address 0011.2233.4455
Bridge ID Priority 32778
Address 0011.2233.4455In a network running STP, SW2 became the root bridge for VLAN 10. Both SW1 and SW2 have the same bridge priority. Why did SW2 become the root?
⚠ Common exam trap
Remember, in STP, lower values are preferred. If priorities match, the MAC address decides the root bridge.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Because SW2 has the lower bridge ID due to the lower MAC address.
SW2 became the root bridge because its bridge ID is lower. In practical terms, spanning tree elects the root bridge by comparing bridge IDs, which are based on priority plus MAC address. The device with the lowest bridge ID wins. In the exhibit, both switches use the same priority, so the tie is broken by the lower MAC address. This is a classic STP interpretation question. Many learners focus only on priority, but if priorities match, the MAC address becomes decisive.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Because SW2 has the lower bridge ID due to the lower MAC address.
Why this is correct
In STP, each switch's bridge ID is composed of a configurable priority (default 32768) and its MAC address, concatenated to form a unique identifier. When SW1 and SW2 have equal bridge priority, the election breaks the tie by comparing the MAC portion, and the numerically lower MAC address wins. Since SW2's MAC is lower, its bridge ID is lower, making it the root bridge for the VLAN.
- ✗
Because SW2 has the higher VLAN number configured.
Why it's wrong here
The VLAN number is simply a Layer 2 segmentation identifier and is never part of the STP root election criteria. STP runs per VLAN (PVST/PVST+) but the decision is based solely on the bridge ID, which combines priority and MAC address, not the VLAN ID. Therefore, having a higher VLAN number configured on SW2 gives it no advantage in becoming the root bridge.
When this WOULD be correct
In a different question setup where the context involves selecting a root bridge based solely on VLAN configuration, such as asking which switch would be preferred if all other factors were equal and only VLAN numbers were considered, this option could be correct.
- ✗
Because SW2 has more trunk ports than SW1.
Why it's wrong here
The number of trunk ports a switch has is irrelevant to STP root bridge selection, because the election uses only the bridge ID, not any measure of port count or bandwidth. Trunk ports affect how BPDUs are propagated but they do not influence which switch is considered the root. Therefore, even if SW2 has more trunks than SW1, that alone cannot make SW2 the root bridge for the VLAN.
When this WOULD be correct
In a different question setup, if the question asked why a switch with the most trunk ports would be preferred for forwarding traffic in a network, then this option could be correct. For example, if the question focused on optimizing traffic flow and redundancy in a network design scenario, the switch with more trunk ports might be favored.
- ✗
Because SW2 has the highest bridge priority.
Why it's wrong here
STP elects the root bridge using the lowest bridge ID, and the bridge priority is the most significant field within that ID. A higher bridge priority actually makes a switch less likely to win the election, because configuration values range from 0 to 61440 in increments of 4096 and lower numbers are preferred. Thus SW2 could not become root because it has the highest bridge priority; that would disqualify it.
When this WOULD be correct
In a different question context where the bridge priority is the only factor being considered, and SW2's bridge priority is indeed higher than that of other switches, this option would be correct. For example, if the question asked which switch would become the root bridge if all other factors were equal but bridge priority was higher for SW2.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓Because SW2 has the lower bridge ID due to the lower MAC address.Correct answer▾
Why this is correct
In STP, each switch's bridge ID is composed of a configurable priority (default 32768) and its MAC address, concatenated to form a unique identifier. When SW1 and SW2 have equal bridge priority, the election breaks the tie by comparing the MAC portion, and the numerically lower MAC address wins. Since SW2's MAC is lower, its bridge ID is lower, making it the root bridge for the VLAN.
✗Because SW2 has the higher VLAN number configured.Wrong answer — click to see why▾
Why this is wrong here
The VLAN number is not a factor in the STP root bridge election. The election is based solely on bridge ID, which consists of bridge priority and MAC address.
★ When this WOULD be the correct answer
In a different question setup where the context involves selecting a root bridge based solely on VLAN configuration, such as asking which switch would be preferred if all other factors were equal and only VLAN numbers were considered, this option could be correct.
Why candidates choose this
Students might confuse VLAN numbering with bridge priority or think that higher VLAN numbers have some influence, but STP operates per VLAN with independent elections.
✗Because SW2 has more trunk ports than SW1.Wrong answer — click to see why▾
Why this is wrong here
The number of trunk ports does not affect the root bridge election. STP uses bridge ID (priority and MAC address) to determine the root bridge, not port count or type.
★ When this WOULD be the correct answer
In a different question setup, if the question asked why a switch with the most trunk ports would be preferred for forwarding traffic in a network, then this option could be correct. For example, if the question focused on optimizing traffic flow and redundancy in a network design scenario, the switch with more trunk ports might be favored.
Why candidates choose this
Some might think that more trunk ports indicate a more central switch, but STP does not consider port count in the election process.
✗Because SW2 has the highest bridge priority.Wrong answer — click to see why▾
Why this is wrong here
The root bridge is elected based on the lowest bridge ID, not the highest. A higher bridge priority (numerically larger) makes a switch less likely to become root.
★ When this WOULD be the correct answer
In a different question context where the bridge priority is the only factor being considered, and SW2's bridge priority is indeed higher than that of other switches, this option would be correct. For example, if the question asked which switch would become the root bridge if all other factors were equal but bridge priority was higher for SW2.
Why candidates choose this
Students may mistakenly think 'highest' means best, but in STP, lower values are preferred for both priority and MAC address.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
Quick reference
Access Control Model Comparison
| Model | Acronym | Who Controls Access? | Best For |
|---|---|---|---|
| Discretionary Access Control | DAC | Resource owner | Small teams, file shares |
| Mandatory Access Control | MAC | System / security labels | Classified govt / military |
| Role-Based Access Control | RBAC | Administrator (via roles) | Enterprise environments |
| Attribute-Based Access Control | ABAC | Policy engine (user + resource attributes) | Fine-grained, dynamic policies |
| Rule-Based Access Control | RuBAC | System rules / ACLs | Firewall rules, network ACLs |
Go deeper
Related to this question
Learn chapter
IPv4 Addressing and Address Classes
Key term
STP
STP (Spanning Tree Protocol) is a network protocol that prevents loops in Ethernet networks by creating a loop-free logical topology.
Key term
Bridge Protocol Data Unit
A Bridge Protocol Data Unit (BPDU) is a special message that network switches exchange to detect and prevent loops in an Ethernet network.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.